The invention relates to a gas diffusion layer for an electrochemical cell, in particular for a PEM electrolysis cell. The invention furthermore relates to an electrochemical cell, in particular a PEM electrolysis cell or galvanic cell having such a gas diffusion layer, and also to an electrolyzer.
Electrochemical cells are generally known and are split into galvanic cells and electrolysis cells. An electrolysis cell is an apparatus in which an electric current causes a chemical reaction, with at least some electrical energy being converted into chemical energy. A galvanic cell is an apparatus complementary to the electrolysis cell for spontaneously converting chemical energy into electrical energy. A known apparatus of such a galvanic cell is a fuel cell, for example.
The cleavage of water by electric current for the production of hydrogen gas and oxygen gas by means of an electrolysis cell is well-known. A distinction is made here primarily between two technical systems, alkaline electrolysis and PEM (Proton-Exchange-Membrane) electrolysis.
The core of a technical electrolysis plant is the electrolysis cell, comprising two electrodes and an electrolyte. In a PEM electrolysis cell, the electrolyte consists of a proton-conducting membrane, on both sides of which are located the electrodes. The assembly consisting of membrane and electrodes is referred to as MEA (Membrane-Electrode-Assembly). In the assembled state of an electrolysis stack composed of a plurality of electrolysis cells, the electrodes are contacted by what are termed bipolar plates via a gas diffusion layer, the bipolar plates separating the individual electrolysis cells of the stack from one another. In this case, the O2 side of the electrolysis cell corresponds to the positive terminal and the H2 side corresponds to the negative terminal, separated by the intermediate membrane-electrode-assembly.
The PEM electrolysis cell is fed on the O2 side with fully desalinated water, which is decomposed at the anode into oxygen gas and protons (H+). The protons migrate through the electrolyte membrane and recombine at the cathode (H2 side) to form hydrogen gas. In addition to the electrode contacting, the gas diffusion layer resting on the electrodes ensures an optimum water distribution (and therefore the wetting of the membrane) and also the removal of the product gases. What is therefore required as a gas diffusion layer is an electrically conductive, porous element with good permanent contacting of the electrode. As an additional requirement, dimensional tolerances which possibly arise in the electrolyzer should be compensated for in order to allow for uniform contacting of the MEA in every instance of tolerance.
To date, sintered metal disks have generally been used as the gas diffusion layer. Although these satisfy the requirements in respect of electrical conductivity and porosity, an additional tolerance compensation of the components of the electrolysis cell on both sides of the gas diffusion layer is not possible. Moreover, the manufacturing costs for such disks are comparatively high and there is a restriction with respect to the size owing to the pressing forces required during the manufacture of such disks. In addition, problems in relation to warping which can only be controlled with difficulty arise in the case of large components.
The use of gas diffusion electrodes with resilient elements for producing an electrical contact in the case of alkaline electrolyzers is described, for example, in WO 2007/080193 A2 and EP 2436804 A1.
EP 1378589 B1 discloses a spring sheet, in which the individual spring elements are bent alternately upward and downward. The spring sheet is incorporated in an ion exchange electrolyzer merely on the cathode side, such that the spring sheet contacts the cathodes directly.
US 2003/188966 A1 describes a further spring component for an electrolysis cell, which is arranged between a partition wall and a cathode. The spring component comprises a multiplicity of leaf spring elements, which rest on the cathode for uniform adaptation.
Further gas diffusion electrodes of differing construction are described in WO 2002035620 A2, DE 10027339 A1 and DE 102004023161 A1.